mockito官方文档地址： https://www.javadoc.io/doc/org.mockito/mockito-core/latest/org/mockito/Mockito.html#30
//using mocks - only mockOne is interacted
mockOne.add("one");
//ordinary verification
verify(mockOne).add("one"); // 验证调用过add one
//verify that method was never called on a mock
verify(mockOne, never()).add("two"); // 验证从未调用过add two
end.